Animated Deep Zoom-in. (Drone style)
To reduce the render time of a large scale scene like that there is a nice new option for object camera culling (Cycles only).

It will remove the visibility of objects from the scene as they move outside of the camera's view, saving rendering computation. If the object moves back in frame the object comes back. It only does this for rendering. The objects will not actually be removed in your .blend file or 3D viewport.


Switch to the Cycles render engine
In the Properties panel go to the Scene tab.
Check the box for Simplify




Then select an individual object:


Go to the object properties panel
Expand the Cycles Settings section
Check Use Camera Cull




Warning: You will have to deal with problems like having shadows and reflections suddenly disappear from the camera's view, because the culling only detects the actual object in the camera's view; not any of its influence (shadows, reflections, etc) on the rest of the scene. Some of this could be fixed using the "Camera Cull Margin" option near the "Use Camera Cull" option in the scene properties (Image 1). The rest will have to be fixed by just being selective about which object you check the cull option on.